I think what we're seeing now is a flip of the script of the Democratic House dominance that started in 1954 and lasted all the way until the 1994 elections.
Democrats only had the White House for 14 of those 40 years, but they held the House for 40 years straight, and usually held the Senate.
Whereas now the Democratic candidate has won the popular vote in 6 of the last 7 elections, while the House has been stubbornly Republican and the Senate has split almost evenly between the two parties.
Compromising this is that the Electoral College has a GOP lean which has fucked us over twice, otherwise you would have seen nearly 30 years of Democrats in the White House broken up only by one Bush term.